Improve keyboard layout spacing and key preview behavior

[jamditis]

Summary

This PR refines the keyboard UI layout and improves the key preview interaction experience by adjusting dimensions, spacing, and adding delayed preview dismissal.

Key Changes

• Layout Spacing: Reduced horizontal padding in extra_row and number_row from 2dp to 1dp, and reduced key margins from 2dp to 1dp for more compact layout
• Key Heights: Increased button heights from 36dp to 40dp across all extra row keys (ESC, Tab, Ctrl, arrow keys, etc.) and number row keys for better touch targets
• Key Preview Behavior:
  • Added delayed dismissal of key preview (300ms) instead of immediate hiding, allowing preview to remain visible briefly after key release
  • Preview hide is cancelled if another key is pressed before the delay completes
  • Added touch slop (4dp) to ACTION_MOVE detection to prevent accidental key deselection during slight finger movements
• Code Refactoring: Introduced previewHideRunnable variable to track and manage delayed preview hide operations

Implementation Details

• The delayed preview hide uses longPressHandler.postDelayed() to schedule dismissal after 300ms
• Touch slop is applied symmetrically to horizontal bounds checking during drag operations
• Preview hide runnable is properly cancelled when a new key press begins, ensuring smooth transitions between key presses

https://claude.ai/code/session_01WRedvWA2k9ZUQtWd2cWEtY